The present invention relates generally to universal joints including a trunnion cross which connects the yoke arms of a pair of yokes, and more particularly, to universal joints of the type including cylindrical bearing bodies or sleeves within bores through the yoke arms, and a number of bearings arranged between projecting portions of the trunnion cross and the bearing sleeves, the sleeves being sealed relative to the body of the trunnion cross by means of a contact seal.
Universal joints are known, such as disclosed in German Pat. No. 2,618,536, wherein a supply of lubricant is provided between an elastic seal which covers the body of the trunnion cross to ensure maintenance-free lubrication during the service life of the joint. This construction is, however, seldom used at the present time for relatively large trunnion crosses since, in such a case, the manufacture of such a joint is not economical. For example, trunnion crosses used in rolling mills have such a relatively large diameter that the costs of coating a plastics material thereon are so high that these crosses can no longer be economically manufactured.
An object of the present invention is to enable a trunnion cross of relatively large diameter to be provided in a universal joint which can be economically manufactured with the use of inexpensive materials but, nevertheless, allow for a supply of lubricant to ensure maintenance-free lubrication during the service life of the joint.
In accordance with the present invention, an elastic seal is provided which closes the ends of the bearing bodies or sleeves which face radially outwardly from the joint axis of rotation so that the seal covers the end face of the projecting portion of the trunnion cross within each yoke arm bore. A supply of lubricant can thereby be contained between the end face of each trunnion portion and the elastic seal.
An advantage of this construction resides in the protection by the elastic seal of the bearing sleeves against penetration of dirt and dust from the outside. The seal also makes possible a pressurized supply of lubricant so that the bearings are continuously provided with a sufficient amount of lubricant during the entire service life of the universal joint shaft.
In order to generate the pressure on the lubricant supply, the elastic seal is placed in the bearing body or sleeve before assembly of the trunnion cross in the yoke arms. The bearing sleeves, as well as a reservoir region adjacent the seal, are filled with lubricant and, after fastening the contact seal, are slid over the projecting portions of the trunnion cross so that excess lubricant flows into the reservoir region, the seal exerting a pressure in the opposite direction which subsequently provides the bearings to be lubricated with lubricant during operation. Oppositely directed centrifugal force, which acts on the lubricant supply during operation of the joint, is counteracted by the pressure provided on the lubricant supply by the seal, so that this centrifugal force has no influence on the lubrication of the bearings during the service life of the joints. It should be noted that universal joint shafts having large diameters of rotation must, as a rule, operate at relatively lower rates of rotational speed than shafts having smaller diameters of rotation, wherein such centrifugal force attains correspondingly smaller values.
In accordance with another feature of the present invention, the elastic seal can be secured within the bearing body or sleeve, or directly within the bore of the yoke arm.
In accordance with still another feature of the invention, the seal is provided with a thickened edge which engages an annular groove formed in the inner wall of the bearing sleeve. In such an embodiment, assembly of the joint including the mounting of the seal can be performed without any special equipment since only a groove extending over the inner circumference of the inner wall of the bearing sleeve is required, and the elastic seal engages this groove with a correspondingly formed annular projection.
In accordance with the invention a further embodiment of the seal is provided, the outer edge of the seal having an annular groove therein which is engaged by a corresponding projection on the radially outer side of the bearing sleeve. As a result, both sealing and securing of the elastic seal are ensured.
In accordance with yet another feature of the invention, a protective cap is also provided for holding the seal in the bearing sleeve, the cap having a cylindrical projection extending through a central opening in the seal to support the projecting portion of the trunnion cross. This enables centrifugal forces, which act on the lubricant during operation, to be absorbed without exerting an additional force on the lubricant supply.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.